Spark plug



APil 2, 1929- H. RABEzzANA 1,707,741

SPARK PLUG A Filed July 20, 1925 3111x1114 oz atto: nu;

Patented Apr. 2, 1929.

UNITED STATES 1,707,141 PATENT oFr-icu.

\ HECTOR RABAEZZANA, F FLINT, MICHIGAN, ASSIGNOR TO A C SPARK PLUGCOMPANY,

' OF FLINT, MICHIGAN, A COMPANY 0F MICHIGAN.

SPARK PLUG.

Application filed July 20, 1925. Serial No. 44,867.

Considerable difficulty has been experienced in maintaining the sparkplugs used in internal combustion engines, particularly those operatedat high compressions, at suiiiciently low temperatures for mosteffective operation. Thus, when the plugs become too highly heated, theelectrical resistance of the insulators is reduced and the temperatureof the latter may even be raised to a point TJ of redness and causepre-ignition of the combustion mixture.

This application discloses one means which may be used to secure or toassist in securing the desired lower-working temperatures for the plug.This means consists primarily in forming the inner surface of the shellof the plug of such configuration that a considerable area is presentedto the surrounding gases whereby the rate of transfer of heat therefromis greatly increased. This increased transfer of heat results in alowering of the temperature of these gases and as they also surround theinsulator, the temperatures to which the latter are subjected arethereby reduced. Specifically, the configuration which I have preferredto employ consists of ridges upon the inner surface of the shell, theridges extending either axially or circumferentially.

Referring now to the drawings:

Figure l is a side elevation ofa spark plug, parts being shown insection to better illustrate the invention;

Figure 2 is an enlarged sectional view of the shell shown in Figure 1;

Figure 3 is a section on line 3-3 of Figure 2;

Figure 4 is a. view corresponding to Figure 2 but showing a modifiedform; and

Figure 5 is a section on line 5-5 of Figure 4. Y v

I have illustrated in the drawing a spark plug of conventional typecomprising a shell 2, insulator 4, center electrode '6 and sideelectrode 8. I have formed the interior of the shell with ridges whichmay extend either longitudinally of the shell as shown at 10 inv.Figures 1, 2, and 3 or circumferentially thereof as shown at l2 inFigures 4 and 5. I have found by actual experiment that a plug soconstructed will be maintained at a lower temperature than a plug havinga shell, the

i inner surface of which is a smooth cylinder. With a plug constructedas described the surface of the interior of the shell is greatlyincreased, giving a greater area for contact with the gases, with theresult that there is an increased fiow of heat from the gases into theshell from whence it is effectively dissipated throughthe cylinder head.As these gases are pocketed in the shell there is very littleopportunity for the operation of convection currents so that the heatthu-s lost is not readily replaced. Accordingly, the gases aremaintained at a lower temperature. lVith the gases at a lowertemperature,'the insulator receives less heat with the advantages abovedescribed.

lVhile I have described constructions in which ridges are provided uponthe interior of the shell it is to be understood that my invention isnot limited to these particular con-- fgurations for others may beemployed to secure the desired increased area; thus the shell may beprovided with protuberances'or the 75 like. 1 While I have given abovethe theory of operation Which seems to me now. to best explain theresults obtained, it is to be understood that there may be otherfactors, such as radiation, which may have an important yeffect insecuring the described results in a manner not now obvious, so that myinvention is not to be understood as limited by the theory of operationdisclosed.

What I claim and desire to secure by Letters Patent is:

l. A spark plug comprisingvan open ended metallic shell adapted to besecured in good heat conducting relation with cooled surfaces of theengine, an insulator in the shell extending approximately to the lowerend vthereof, an electrode on the insulator, an electrode on the shell,the lower end of said shell and the lower end of said insulator definingan elongated chamber normally filled with hot combustion gases,substantially the entire surface of the shell exposed in said chamberbeing roughened to increase the area thereof to facilitate theconducting away of heat to prevent said insulator and its electrode fromattaining sufficiently high temperatures to cause pre-ignition.

2. A spark plug comprising an open ended metallic shell adapted to besecured in good heat conducting relation with cooled surfaces of theengine, an insulator in the shell, an electrode on the insulator, anelectrode on the shell, said electrode being arranged to provide a sparkgap outside of the shell, 11 o the lower end of the shell cooperatingwith the insulator to form an elongated annular space extendingsubstantially to the end of the shell, and normally filled with hotcornbustion gases, the portion of the shell eX- posed in said spacebeing provided with corruwations to increase the area thereof to moreellectively conduct away the heat of said gases and prevent the centerelectrode and the insulator from attaining sutliciently highteniperatures to cause pre-ignition.

3. A spark plug comprising a metallic shell adapted to he secured ingood heat conducting rela/tion with cooled surfaces of the engine, aninsulator in the shell, the lower.

end of said shell and the lower end of said insulator being spaced fromeach other tlnoughout a considerable portion of their length anddefining an annular dead air space normally lilled with-hot combustiongases, the surface of the shell opposite the insulator being formed topresent greatly increased area to the said A.dead air space to facilitate conduction of'he'at away from said space, said plug beingprovided with the spaced electrodes arranged to provide a spark gapbelow the lower end ot the shell.

4. A spark plugY comprising.,r a metallic shell adapted to be secured ingood heat conducting relation with cooled surfaces of the engine, aninsulator in the shell, the lower ends of said shelland insulator beingspaced to provide an elongated annular dead air space normally illedWith combustion gases, said insulator being provided with a centerelectrode having its end extending below the shell, said plug beingprovided with an electrode cooperating with the end ot said eenterelectrode to provide a spark gap, the interior of the shell surroundingsaid insulator being formed to provide greatly increased surface toincrease the rate otl conduction ot heat away from said air space.

5. A spark plug comprising a metallic shell adapted to be secured ingood heat conducting relation with cooled surfaces oit the engine, aninsulator in the shell, the lower ends of said shell and insulator beingspaced throughout a considerable portion of their length to form anelongated dead air space normally filled with combustion gases, theinterior surface of the said last named portion of the shell beingprovided with vertical corrugations to increase the rate of conductionof heat away from said space.

ln testimony whereof l alix my signature.

HECTOR RABEZZANA.

